US2286869A - Magnesium base alloy - Google Patents

Description

Patented June 16, 1942 MAGNESIUM BASE ALLOY John C. McDonald,.Midland, Mich., assignor to The Dow Chemical Company, Midland, Mich-., a corporation of Michigan No Drawing. Application December 23, 1940, Serial No. 371,378

4' Claims.

The invention relates to magnesium base alloys, and more particularly concerns an alloy of this nature having a high degree of formability associated with correspondingly high yield and tensile strengths.

Magnesium base alloys are being widely used in the structural arts where a light weight metal is highly desirable, such as for use in making castings, fcrgings, and the like. However, the use of these alloys in the rolled form to make sheet metal articles requiring forming operations, such as bending and drawing, has not progressed as rapidly due to the fact that, in general, alloys having good formability or ductility, permitting relatively sharp bends to be made without the article developing external cracks, usually have inferior characteristics as regards-their 0.3 per cent of .cerium, and 5 per cent of thal-' lium, the balance being magnesium.

The following table, listing some of the properties of rolled sheet metal made from my new quaternary alloy, and comparing these properties with those of closely related ternary alloys,

illustrates the improvement in tensile and yield strengths of my new alloy over similar properties of related alloys.

In the table, the per cent elongation is to be regarded as the measure of ductility or formability of the alloys.

tensile and yield strengths.

It is, accordingly, the principal object of the invention to provide a magnesium base alloy which can be made into rolled sheet and the like possessing a high degree of ductility or form-' ability at ordinary temperatures, enabling it to be sharply bent, drawn, or otherwise shaped, while having high tensile and yield strengths.

Other objects and advantages will be apparent as the description of the invention proceeds.

My invention resides in the discovery that a magnesium base alloy containing from about 0.4 to 12 per cent of aluminum, 0.01 to 1 per cent of cerium, and from 1 to 15 per cent of thallium possesses the aforementloned'desirable properties. The term magnesium used herein and in the appended claims is intended to include magnesium containing the ordinary impurities present in the commercially pure metal, such as traces of iron, nickel, copper, and silicon. While the properties of high tensile and yield strengths, coupled with excellent formability, are manifest over the entire range of composition indicated,

I have found that, in general, compositions DOS-'65 The properties set forth above under the term Lannealed were obtained by first rolling specimens of the alloys at a temperature of between 450 to 550 F., and thereafter annealing them at various temperatures in a range of from 400 to 800 F. The properties selected for the table were those .of the annealed specimens which exhibited the maximum elongation. The properties set forth under the term "cold rolled were obtained by subjecting specimens of the alloys which had first been hot rolled at temperatures of 450 to 550 F. to additional rolling in the cold state. The properties selected for the table were those of the cold rolled specimens which exhibited the greatest tensile and yield strengths, while having at least a 1 per cent elongation in two inches.

A comparison of the properties listed in the table shows that the combined properties of my new polynary alloy are superior to those of the related alloys. For example, it will be noted that the yield and tensile strengths in the annealed and the cold rolled state show a general improvement over similar properties of related alloys, while the per cent elongation, which is to be regarded as a measure of the ductility or formability of the alloy, is of a high order, thus rendering the alloy suitable for use in forming operations. A corresponding improvement is ex,- hibited throughout the composition range or alloying ingredients indicated.

While the new alloy is most useful in wrought form due to its formability characteristics coupled with high strength properties, it may also be suitably used for making castings, extruded forms, and the like. It is further pointed out that the new alloy is amenable to solution and precipitation heat treatments, which, accordingly, modify its properties.

It has further been discovered that manganese may be added to the magnesium-cerium-aluminum-thallium alloy above described without substantially altering the formability characteristics. The presence of the manganese improves the yield and tensile strengths of the alloy and at the same time improves the corrosion characteristics of the alloy and thus makes its'addition desirable. The following table lists the properties of rolled sheet made from my new alloy having manganese added thereto.

Misch-metal. Magnesium-cerium alloys are commonly made up by employing Mischmetal as a source of cerium. It is sometimes desirable to add more than the theoretical amount of Misch-metal, since the alloying efiiciency is not always 100 per cent and some loss may be intain an alloy containing more than 1.0 per cent of manganese. In compositions containing more aluminum, such as from 8 to 12 per cent, it is difficult to obtain an alloy containing more than 0.5 per cent of manganese.

It is to be understood that the invention is not to be limited to the specific composition herein described, but may take other forms without departing from the scope of the invention.

I claim:

1. A magnesium base alloy containing from 0.4 to 12 per cent of aluminum, from 0.01 to 1 per cent of cerium, and from 1 to 15 per cent of thallium, the balance being magnesium.

It is evident from examination of the properties listed in the table that the formability characteristics are not substantially impaired by the addition of manganese, while the tensile and yield strengths show improvement over the related alloys without manganese.

The new alloy may be compounded by any of the methods usually employed for alloying metals with magnesium, such as by adding the alloying ingredients singly or jointly to a bath of molten magnesium, which is preferably protected from oxidation by a suitable flux. The cerium may be added to the alloy as such, or in the form of and from 0.01 to 3.0 per cent of manganese, the

balance being magnesium.

4. A magnesium base alloy containing 6 per cent of aluminum, 0.3 per cent of cerium, and 5 per cent of thallium.

' JOHN C. MCDONALD.